Pressurized backwash filter

ABSTRACT

A liquid filtering and backwashing apparatus is disclosed comprising a pressurized filter tank having a first outlet valve and a filter cell disposed within the filter tank. The filter cell includes a conduit and an outer member with the outer member spaced apart relative to the conduit with a filtering medium positioned between the conduit and the outer member. A plurality of openings in the outer member enable fluid communication between the liquid to be filtered in the filter tank and the filtering medium. The conduit is provided with a plurality of slits to enable the pressure in the tank to force fluid communication between the filtering medium and interior of the conduit while retaining the filtering medium external the conduit. Means are provided to vary the size of the slits to adjust for differing pressures or filtering requirements. A backwash holding tank in fluid communication with the conduit collects the filtered liquid. The backwash holding tank includes a second outlet valve for the filtered liquid to drain. When the filter cell becomes clogged with the filter clogging material the first outlet valve is opened, the second outlet valve is closed, and the backwash holding tank is provided with compressed gas through an inlet valve forcing filtered liquid back into the filter cell and filter tank thereby backwashing the filter cell and filter tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of Ser. No. 229,695, filed Aug. 8, 1988,now abandoned, which in turn is a continuation of Ser. No. 049,840,filed May 15, 1987, now U.S. Pat. No. 4,818,420, dated Apr. 4, 1989.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a pressurized filter and backwashingapparatus. More specifically, a granular pressure sensitive filter and abackwashing apparatus and method using filtered liquid under pressure isdisclosed.

2. Description of the Prior Art

Granular filters are very effective in removing solid material from aliquid flow. However, the filter looses usefulness as it becomesimpaired by the deposition and entrapment of filter clogging material.The success of any granular filter depends on the ease and on the extentwhich the filter can be cleaned. Granular filters also rely on influentwater to pass through the filter and into a pipe. The pipe isconstructed with slits for gathering the filtered water. These slitsmust be small enough to prevent the sand from gaining entrance, yetlarge enough for the fluid to pass.

The prior art utilizes numerous structures and flow patterns in order toenhance the ease and extent a clogged filter can be made useful. In anearly process an outer portion of a rotatable cylinder comprising aninner and outer wire mesh cylinder which holds a filtering materialbetween the wire mesh cylinders enables the influent to flow into theinterior of the rotatable drum through the filtering medium and into areservoir as cleaned water. As the filtering medium begins to clog, thelevel of influent water within the drum rises to trigger a motor whichrotates the drum filtering means. Effluent cleaned water is then pumpedfrom the effluent reservoir and sprayed upon the filtering means to washit free of the clogging material. The contaminated backwash water isdirected to an outflow by means of a trough within a cylinder. As theinfluent level falls the rotatable cylinder stops rotating therebyending the backwash process.

In another prior art process for cleaning a sand filter, the water to beclarified passes upward through a sand filter and accumulates above thesand filter as clarified water which is allowed to drain off. Forcleaning the sand filter, the process was essentially reversed.

In another process, a specially designed gravity filter apparatusprevents the filtering material from passing along with the effluentduring the backwashing process. The backwashing process utilizes awashing liquid generally a water and gas mixture and passes this mixtureupward through the filter to create a water-gas emulsion which loosensthe clogging material from the filter.

In another gravity sand filter, the backwashing process utilizes abackwash fluid comprising water or water with air which is pushed upthrough the filter and removed from the filtering apparatus by overheadtroughs.

The prior art systems are complex in structure, difficult to use andallow a portion of the filter clogging material to fall back onto thefilter surface after the backwashing process.

It is a primary object of this invention to provide a filter andbackwash apparatus and method which permits the filtered liquid to beused directly for backwashing the filter cell and filter tank.

It is a further object of this invention to provide a filter andbackwash apparatus which is simple in design and economical to operate.

It is a further object of this invention to provide a filter andbackwash apparatus which utilizes relatively a small amount of filteredwater in the backwashing process.

It is a further object of this invention to provide a filter andbackwash apparatus which is simple to operate.

It is a further object of this invention to provide a filter andbackwash system which cleans the filtering medium and filter tank duringthe backwash process.

It is a further object of this invention to provide a filter andbackwash process capable of manual or automatic backwash initiation andtermination.

It is a further object of this invention to provide a filter cell whichenables radial filtration and radial backwashing about the length of thefilter cell.

It is a further object of this invention to provide a backwashingapparatus which prevents the clogging material removed from the filtercell and filter tank by backwashing to settle back onto the filter cellor back into the filter tank.

The effectiveness and time of backwashing is related to the amount ofwater which flows out of the collection tube and back through the filterelement. This, in turn, is controlled by the opening size of the holesor slits in the tube. For back washing large openings are desirable.However, as discussed previously, if the opening is too large, sand willclog the opening and the system will not perform properly.

It is a still further object of this invention to provide a filtrationelement which can allow filter water to pass through it while stillallowing back flow washing.

It is a further object of this invention to provide a filtration elementwhich has a collection tube allowing varying amounts of liquid to passinto or out of the tube.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed to be merelyillustrative of some of the more pertinent features and applications ofthe invention. Many other beneficial results can be obtained by applyingthe disclosed invention is a different manner of modifying the inventionwithin the scope of the disclosure. Accordingly, other objects and afuller understanding of the invention may be had by referring to thesummary of the invention and the detailed description describing thepreferred embodiment in addition to the scope of the invention definedby the claims taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The liquid filter and backwash apparatus of the present invention isdefined by the appended claims with specific embodiments shown in theattached drawings. For the purpose of summarizing the invention, theinvention relates to a pressurized liquid filtering and backwashingapparatus and to a method of liquid filtering and backwashing to removesuspended particles such as silt, mud, sand and the like from a liquidsuch as water. The liquid filtering and backwashing apparatus includes apressurized filter tank, having a first and second end, to receive theliquid to be filtered from a means for admitting the liquid to befiltered into the filter tank. A filter cell, having a first and secondend, is disposed within the filter tank. A conduit with a first end, amid-point, and a second end has an inner passageway extending from thefirst end of the conduit through the second end of the conduit. Thesection of the conduit which extends between the first end and themidpoint defines a first portion of the conduit. Whereas, a section ofthe conduit which extends from the mid-point of the conduit to thesecond end of the conduit defines a second portion. The first portion ofthe conduit is provided with a plurality of openings, which can beadjustable as to size, to enable fluid communication the innerpassageway of the conduit and the filtering medium while retaining thefiltering medium external the conduit. The filter cell includes thefirst portion of the conduit and an outer member. The outer member isspaced apart relative the first portion of the conduit. The outer memberincludes a first end and a second end. A filtering medium is positionedbetween the first portion of the conduit and the outer member of thefilter cell to entrap filter clogging material from the liquid to befiltered thereby forming a filtered liquid. The conduit provides theinner passageway to enable fluid conveyance or communicationtherethrough. The first end of the filter cell includes the first end ofthe outer member and the first end of the conduit. The second end of thefilter cell includes the second end of the outer member. The first andsecond ends of the filter cell are sealed in order to contain thefiltering medium between the conduit and the outer member of the filtercell and to seal the liquid to be filtered from the inner passageway ofthe conduit by a route other than passing through the outer member andfiltering medium of the filter cell. A plurality of openings in theouter member enable fluid communication with the filtering medium. Theouter member is positioned around and spaced from the conduit to retainthe filtering medium internal the outer member. A backwash holding tankin fluid communication with the second portion of the conduit andcollects the filtered liquid flowing from the conduit. The first end ofthe filter tank includes a first outlet valve positioned to enableoutward flow from the filter tank. The backwash holding tank includes asecond outlet valve to enable the filtered liquid to drain from theholding tank. The backwash holding tank includes an inlet valve to admitcompressed gas into the holding tank after opening the first outletvalve of the filter tank and closing the second outlet valve of theholding tank to enable backwashing of the filter cell and filter tankutilizing the filtered liquid collected in the backwash holding tank.

In a preferred embodiment the openings in the conduit are long narrowopenings or slits. In another embodiment the opening size is adjustable.

In another embodiment of the invention the filter tank includes aV-shaped bottom to aid in drainage and removal of the filter cloggingmaterial from the tank. The filter tank includes a first end and asecond end with the first end of the V-shaped bottom being lowerrelative the second end of the V-shaped bottom resulting in a slopingdownward configuration whereby liquid flow along the bottom of thefilter tank is enhanced. The first outlet of the filter tank ispositioned proximate the first end of the V-shaped bottom to enhanceoutward flow from the filter tank during the backwashing process. In apreferred embodiment of the invention the filter cell is positionedparallel to the sloped V-shaped bottom of the filter tank with the firstend of the filter cell being positioned proximate the first outlet valveof the filter tank to further enhance the outward flow from the filtertank during the backwashing process. This position also enables thefiltered water to be decanted, to an extend, when it flows out of theconduit and into the holding tank. That is, any sediment or the likewhich may enter the conduit tends to collect at the lower first end ofthe conduit with the filtered liquid draining off from the upper secondend of the conduit and into the backwash holding tank.

The conduit provides a passageway through which fluid is conveyed. Thefirst portion of the conduit is provided with a plurality of openings,preferably a plurality of slits, about the surface of the pipe. Theseopenings provide a fluid passage between the filter medium and the firstportion of the conduit by either the filtered liquid or the cleansingliquid.

The outer member is provided with a plurality of openings of asufficient size to permit the retention of the filtering medium internalthe outer member while allowing fluid communication therethrough.Preferably, the outer member comprises either a wire mesh, such as ascreen, or a perforated sleeve. Preferably, the openings in the outermember are about 0.01 inches.

In another embodiment of the invention the filtering medium is granular.The preferred granular size of the granular filtering medium has adiameter of about 0.02 to 0.03 inches with the openings formed in theouter member of the filter cell having a diameter of about 0.01 inchesand with the plurality of slits provided in the first portion of theconduit of the filter cell being long cuts having a width of about 0.01inches. The most preferred granular filtering medium is sand.

The preferred shape of the conduit and outer member is cylindrical.

In one embodiment the filter and backwash apparatus further includes afloat switch control means positioned in the filter tank to activate thebackwash process. The float switch is activated when a second level inthe filter tank is reached by the liquid to be filtered. This indicatesthat the filtering medium is clogged thereby impeding the flow of theliquid to be filtered through the filter cell resulting in the liquid tobe filtered rising to the second level. At this level the first outletvalve of the filter tank is opened, the second outlet valve of theholding tank is closed and the inlet valve is opened to admit compressedgas into the holding tank to initiate the backwash process. In mostpreferred embodiment a timing means activated by the float switchcontrol means closes the first outlet valve and the inlet valve andopens the second outlet valve after a preset period of time to terminatethe backwash process thereby enabling the filtering process to restart.

In another embodiment the liquid to be filtered is treated effluent froma sewage treatment plant. In this application the first outlet valve isin fluid communication with a mud well or reservoir which is in furtherfluid communication with the sewage treatment facility. This enables theflow from the first outlet valve, which comprises filter cloggingmaterial and other particles or sediment from the bottom of the filtertank which are suspended or mixed with the cleansing water or liquidduring the backwash process, hereafter referred to as "spent backwashliquid", together with a limited amount (from the filter tank) of liquidto be filtered, to be removed or discharged from the filter tank toenter the mud well and be pumped back to the sewage treatment plant forfurther treatment.

In a preferred embodiment of the invention a filter tank for receivingthe liquid to be filtered includes a first end and a second end. Thefirst end of the filter tank includes a first outlet valve to enable inuse an outward flow from the filter tank. The filter tank includes aV-shaped bottom to further enhance in use the outward flow from thefirst outlet valve of the filter tank. The V-shaped bottom furtherincludes a first end and a second end with the first end of the V-shapedbottom being lower relative the second end of the V-shaped bottom toaugment outward flow from the filter tank. The first outlet of thefilter tank is positioned proximate the first end of the V-shapedbottom. A filter cell for filtering the liquid to be filtered includes afirst end and a second end and is disposed within the filter tank in aparallel manner relative to the V-shaped bottom. A conduit has a firstend, a midpoint, and a second end with the section of the conduit whichextends between the first end and the midpoint defining a first portionof the conduit. A section of the conduit which extends from themid-point of the conduit to the second end of the conduit defines asecond portion. The first portion of the conduit is provided with aplurality of openings to enable fluid communication with the innerpassageway of the conduit and the filtering medium while retaining thefiltering medium external the conduit. The filter cell includes an outermember and the first portion of the conduit. The outer member includes afirst end and a second end. The filter cell includes a first end and asecond end, with the first end of the filter cell including the firstend of the outer member and the first end of the conduit, with thesecond end of the filter cell including the second end of the outermember. The outer member of the filter cell is spaced apart relative tothe first portion of the conduit. A filtering medium positioned betweenthe first portion of the conduit and the outer member entraps filterclogging material from the liquid to be filtered thereby forming afiltered liquid. The first and second ends of the filter cell are sealedsuch that the filtering medium is contained between the first portion ofthe conduit and the outer member. The first portion of the conduit isprovided with a plurality of openings to enable fluid communication withthe inner passageway of the conduit while retaining the filtering mediumexternal the first portion of the conduit. A plurality of openingsformed in the outer member to enable fluid communication with thefiltering medium. A backwash holding tank collects the filtered liquid.The second portion of the conduit extending into the backwash holdingtank provides fluid communication between the backwash holding tank andthe first portion of the conduit. A mud well is positioned below thefilter tank to receive the outward flow from the first outlet valve ofthe filter tank of spent backwash liquid. The backwash holding tankincludes a second outlet valve to enable the filtered liquid to drainfrom the holding tank. The backwash holding tank includes an inlet valveto admit compressed gas into the holding tank after the second outletvalve of the holding tank is closed and the first outlet valve of thefilter tank is opened to enable backwashing of the filter cell andfilter tank.

In another embodiment a method of filtering and backwashing comprisesproviding a liquid filtering and backwashing apparatus including afilter tank with a first outlet valve. A conduit which includes a firstportion and a second portion is disclosed. A filter cell which includesthe first portion of the conduit and an outer member with the outermember being positioned around and spaced apart from the first portionof the conduit. A filtering medium is positioned between the firstportion of the conduit and the outer member. The first portion of theconduit is provided with a plurality of openings to permit fluidcommunication therethrough, the outer member retains the filteringmedium proximate the first portion of the conduit and has a plurality ofopenings formed therein to enable fluid communication therethrough. Thefirst portion of the conduit of the filter cell and the outer member ofthe filter cell are disposed within the filter tank. The second portionof the conduit is in fluid communication with a backwash holding tankhaving a second outlet valve and an inlet valve. A filter and backwashoperation is conducted by introducing a liquid to be filtered into thefilter tank until the liquid to be filtered reaches a first level whichenables the liquid to be filtered to cover the filter cell therebyenabling the liquid to be filtered to flow radially inward through theplurality of openings of the outer member and into the filtering mediumwhich entraps the filter clogging material thereby forming a filteredliquid. During the filtering process the filtered liquid passes throughthe plurality of openings formed in the first portion of the conduit andis conveyed by the second portion of the conduit into the backwashholding tank whereby the filtered liquid is collected to the firstlevel. When the filtered liquid reaches the first level, the filteredliquid drains from the backwash holding tank through a second outletvalve positioned at the first level. Periodically the filteringoperation is terminated when the liquid to be filtered in the filtertank reaches a second level in the filter tank. The second levelindicates that the filtering medium is clogged and therefore impedingthe flow of the liquid to be filtered through the filter cell resultingin the liquid to rise from the first level to the second level. Uponreaching the second level a backwash operation is conducted by openingsthe first outlet valve of the filter tank, closing the second outletvalve of the backwash holding tank and opening the inlet valve to acompressed gas source. The compressed gas forces the filtered liquidcollected in the backwash holding tank as a cleansing liquid into theconduit, through the openings of the conduit, through the filteringmedium and through the plurality of openings of the outer member wherebythe material clogging the filtering medium is loosened and forcedradially outward from the filter cell and into the filter tank. Thecleansing liquid and clogging material from the filter tank isdischarged through the first outlet valve thereby backwashing the filtercell and the filter tank. The filtering process is restarted by closingthe first outlet valve of the filter tank and the gas inlet valve of thebackwash holding tank and by opening the second outlet valve of thebackwash holding tank.

Preferably the method includes a float switch control means positionedin the filter tank to automatically close the second outlet valve of theholding tank, to open the first outlet valve of the filter tank and toopen the inlet valve of the holding tank to admit compressed gas intothe holding tank when the second level is reached in the filter tank toinitiate the backwashing process. Most preferably the float switchcontrol means includes a timing means activated by the float switchcontrol means to close the first outlet valve and the inlet valve and toopen the second outlet valve after a preset period of time to restartthe filtering process.

In a preferred embodiment of the pressurized filter, the influent fromthe sewage treatment plant is pumped into the filter at approximately 15psi pressure. The pressurized liquid is forced through the filter andinto the conduit as discussed above. In place of the level control, apressure monitoring device is installed within the filter when thepressure rises, indicating a clogged filter, the switch activates andthe same procedure is followed as if the level switch had beenactivated.

During the backwash operation, the slot opening size can be adjusted, ifdesired, so that more water will flow backwards through the filter tohelp remove clogged material. Likewise, if it is desired to increase thepurity of the water, the conduit slot size can be reduced and the inputpressure increased.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that conception and the specificembodiment disclosed may be readily utilized as a basis for modifying ordesigning other structures for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of the backwashing filter apparatus;

FIG. 2 is a top view of a backwashing filter apparatus shown in FIG. 1;

FIG. 3 is a partial front view of the backwashing filter apparatus takenalong line 3--3 of FIG. 1;

FIG. 4 is a partial sectional view of the filter cell taken along line4--4 of FIG. 1;

FIG. 5 is a schematic flow chart showing the fluid flow in thebackwashing filter apparatus;

FIG. 6 is a block diagram showing the interconnection of the controlunit and the valves controlled by the output of the control unit; and

FIG. 7 is a cross-sectional view of the preferred embodiment of thepressurized backwashing filter apparatus.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DISCUSSION

FIG. 1 illustrates a cross-sectional view of a liquid filter andbackwashing apparatus 10 according to one embodiment of this invention.The liquid filtering and backwashing apparatus 10 comprises a filtertank 20 for receiving the raw fluid which is to be filtered 14,hereinafter to referred to as "liquid to be filtered," from a sewagetreatment plant 16 by conduit 12. The liquid filter and backwashingapparatus 10 further includes a backwash holding tank 60 for collectingthe filtered liquid 18 and a mud well 80 for holding liquid to bereturned to the sewage treatment plant 16. In one embodiment the filtertank 20 is separated from the backwash holding tank 60 by a wall 22whereas the filter tank 20 is separated from the mud well 80 by a wall22A. The backwash holding tank 60 is separated from the mud well 80 by awall 22B.

The apparatus 10 includes a filter cell 34 having a first end 36 and asecond end 38 positioned within the filter tank 20. The filter cell 34includes an outer member 40 having a plurality of openings 42 formedtherein. The plurality of openings 42 enable fluid communication with afiltering medium 46 located within the filter cell 34. The filter cell34 also includes a conduit 48 having a first end 50 a mid-point 52 and asecond end 54 with a plurality of slits 56 formed in the conduit 48between the first end 50 and the mid-point 52 thereof. The first end 50of the conduit 48 is positioned proximate the first end 36 of the filtercell 34 whereas the mid-point 52 of the conduit 48 is positionedproximate the second end 38 of the filter cell 34. The portion of theconduit 48 which extends between the first end 50 of the conduit 48 andthe midpoint 52 of the conduit 48 defines a first portion 53 of theconduit 48. Whereas, a second portion 55 of the conduit 48 is located inthe backwash holding tank 60 and extends from the midpoint 52 of theconduit 48 to the second end 54 of the conduit 48. Midpoint 52 is thatpoint along conduit 48 positioned somewhere between the first end 50 andthe second end 54 of conduit 48 and is not necessarily at a pointmid-way between the ends 50,54 of conduit 48. The liquid in the backwashholding tank 60 of the apparatus 10 is referred to as the filteredliquid 18. The outer member 40 of filter cell 34 is partially cut awayto illustrate the filtering medium 46 and the first portion 53 of theconduit 48 with a plurality of slits 46 formed in the first portion 53of the conduit 48.

The backwash holding tank 60 collects the filtered liquid 18 from thesecond end 54 of the conduit 48. A second outlet valve 64 positioned inthe backwash holding tank 60 determines the maximum liquid height 66 inthe backwash holding tank 60 since valve 64 preferably provides the onlydrain from the apparatus 10 during the filtering process. Preferably,the maximum liquid height 66 in the backwash holding tank 60 is the samelevel as the liquid height 68 in the filter tank 20 with both levelsbeing equal and defining a first level 70. The second outlet valve 64 ofthe backwash holding tank 60 controls and enables the collected filteredliquid 62 in excess of the first level 70 to drain from the backwashholding tank 60 and into a filtered liquid reservoir 74. The backwashholding tank 60 further includes an inlet valve 76 connected to a sourceof compressed gas 78. The backwash holding tank 60 of the apparatus 10is preferably a sealed tank as shown.

The filter tank 20 of apparatus 10 further includes a first outlet valve21 providing fluid communication from the filter tank 20 to the mud well80. The mud well 80 holds the liquid obtained as a result of thebackwashing process referred to as spent backwash liquid 84. A return 86pumps the spent backwash liquid 84 through a conduit 88 to the sewagetreatment plant 16 to maintain a level 89 of the spent backwash liquid84 in the mud well 80 below a third level 90.

The liquid to be filtered 14 is introduced into the filter tank 20 suchthat the first level 70 is reached. The position of the first level 70is determined by the position of the second outlet valve 64 of thebackwash holding tank 60. At the first level 70, the filter cell 34 iscovered by the liquid to be filtered 14. The liquid to be filtered 14flows through the plurality of openings 42 formed in outer member 40 ofthe filter cell and into the filtering medium 46 where solid impuritiesare removed by the action of the filtering medium 46 to result in afiltered liquid 18. The filtered liquid 18 flows from the filteringmedium 46 through a plurality of long narrow slits 56 formed in thefirst portion 53 conduit 48 into the interior passageway 49 of theconduit 48. The filtered liquid 18 then flows from the first portion 53of the conduit 48 to the second portion 55 of the conduit 48 and intothe backwash holding tank 60. The filtered liquid 18 flows into thebackwash holding tank ultimately reaching the second outlet valve 64where the filtered liquid 18 flows into the filtered liquid reservoir74. Preferably, when the liquid 18 flows out outlet valve 64 the firstlevel 70 is reached in the filter tank 20 and the backwash holding tank60. The first level 70 is maintained by inputting a quantity of liquidto be filtered 14 via conduit 12 and outputting a similar quantity offiltered liquid 18 via valve 64.

When the level of the liquid to be filtered 14 in the filter tank 20reaches a second level 72, this indicates that the filter cell 34 isbecoming clogged thus slowing the filtering movement of the liquid to befiltered 14 through the filter cell 34. With reference to the liquidlevel in the filter tank 20, the operating level or first level 70 isbelow the backwash or second level 72. In order to remove the filterclogging material a backwashing process is initiated. First outlet valve21 of the filter tank 20 is opened to allow the liquid to be filtered 14to flow into the mud well 80 thereby emptying the filter tank 20. Thesecond outlet valve 64 of the backwash holding tank 60 is closed. Theinlet valve 76 of the backwash holding tank 60 opens to admit compressedgas 78 into the holding tank 60 to force the filtered liquid 18 (nowcharacterized as a cleansing liquid 19) back into conduit 48 of filtercell 34, then back into and out of the filter cell 34, into the filtertank 20 and through the open first outlet valve 21 and into the mud well80. The cleansing liquid 19 is characterized as spent backwash liquid 84as it exits the filter tank 20 via the first outlet valve 21 of filtertank 20. The mud well 80 acts as a reservoir for the spent backwashliquid 84. The spent backwash liquid 84 is returned to the sewagetreatment plant 16 by means of a mud well 80 return pump 76 forretreatment.

FIG. 2 is a cross-sectional top view of separate backwashing filterapparatus 10, 10A illustrating two filter cells 34,34A within theirrespective filter tanks 20,20A. A description of one of the backwashingfilter apparatus 10 described the other apparatus 10A. Each filter cell34,34A has similar features. Filter cell 34A is positioned in the filtertank 20A with the first end 36A proximate the first outlet valve 21A.The first portion 53A of conduit 48A is surrounded by the filteringmedium 46A with the outer member 40 of the filter cell enveloping thefiltering medium 46. Filter cell 34A further illustrates the filter cellwith both the outer member 40 and a portion of the filtering medium 46removed in order to display the first portion 53A of conduit 48A. Theouter member 40 of the filter cell 34 is positioned around and extendsslightly more than the length of the first portion 53 of the conduit 48.Filter cell 34 is sealed 37,39 at its first end 36 and its second end38, respectively, in order to contain the filtering medium 46 betweenthe first portion 53 of the conduit 48 and the outer member 40 of thefilter cell. In a like manner, the first 36A and second 38A ends of thefilter cell 34A are sealed 37A, 39A, respectively. The seal 37, 39 atthe first end 36 and second end 38 of the filter cell 34 comprisesmaterial such as the screening of outer member 40. The second portion55,55A of each conduit 48,48A exits each filter cell 34, 34A in order toprovide fluid communication with their respective backwash holding tank60, 60A.

The backwash holding tank 60 is in fluid communication with the secondend 54 of conduit 48 of the filter cell 34. The volume of the backwashholding tank 60 is generally an amount sufficient to fill the volume ofthe inner passageway 49 of conduit 48 during the backwash process. Theheight of the second outlet valve 64 in the backwash holding tank 60determines the first level 70 of the filtered liquid 18 in the backwashholding tank 60 and filter tank 20. The filtered liquid 18 collects inthe backwash holding tank 60 until the first level 70 is reached atwhich level the filtered liquid 18 begins to flow out of second outletvalve 64 and into the filtered liquid reservoir 74. When the liquid tobe filtered 14 in the filter tank 20 is at the first level 70 the filtercell 34 is covered by the liquid to be filtered 14.

The liquid to be filtered 14 is introduced through conduit 12 into thefilter tank 20. The liquid to be filtered 14 enters the filter cell 34through the plurality of openings 42 formed in the outer member 40 ofthe filter cell 34. The liquid to be filtered 14 when passes through thefilter medium 46 wherein solid impurities are removed by the action ofthe filtering medium 46. The now filtered liquid 18 then enters theconduit 48 of the filter cell 34 through a plurality of slits 46 formedin the first portion 53 of the conduit 48 as filtered liquid 18. Thefiltered liquid 18 drains from the second end 54 of the conduit 48 intothe backwash holding tank 60 of the apparatus 10. So long as the liquidto be filtered 14 passes through the filter medium 46 and the secondoutlet valve 64 of the backwashing holding tank is open, the level ofthe liquid to be filtered 14 in the filter tank 20 remains at asubstantially constant first level 70 in the filter tank 20 and in thebackwash holding tank 60 of the apparatus 10.

An inlet valve 76 is positioned in the backwash holding tank 60 andprovides an inlet for compressed gas 78. The compresses gas 78 forcesthe filtered liquid 18 in the backwash holding tank 60 to flow back intothe second end 54 of conduit 48, through the plurality of slits 46formed in the first portion 53 of the conduit 48, radially outwardthrough the filtering medium 46 and radially outward through theplurality of openings 42 in the outer member 40 of the filter cell 34and into the filter tank 20 to flow out the first valve 21 and into mudwell 80. The second portion 55 of conduit 48 of backwash holding tank 60is preferably positioned proximate the bottom of backwash tank 60 anddoes not have formed in its surface a plurality of slits such as theslits formed in the first portion 53 of conduit 48. This enhances thecleansing operation by making use of essentially all of the liquid 18 inthe backwash tank 60.

FIG. 3 is a back view of the backwashing filter apparatus 10, 10A withtheir respective filter tanks and backwash holding tanks separated by acommon wall 22C, 22D respectively illustrating the V-shaped bottom 29 offilter tank 20 with first outlet valve 21 interconnecting the filtertank 20 and mud well 80. A return pump 86 is positioned on the floor 92of the mud well 80. A conduit 88 is connected to pump 86 to return thespent backwash liquid 84 to the sewage treatment plant 16.

A conduit 12 or other means for admitting the liquid to be filtered intothe filter tank, such as a trough, is positioned to enable flow into thefilter tank 20. The filter tank 20 may be open at the top 32 to permitaccess by the conduit 12 to the filter tank from any top position.

Preferably, the filter tank 20 preferably is sloped downward 27 towardthe first end 24 such that the outward flow of the cleansing liquid 19is directed towards the first outlet valve 21. Preferably, the bottom offilter tank 20 is V-shaped 29 in order to further enhance the outwardflow of the cleansing liquid 19 from the filter tank 20. Mostpreferably, the bottom of filter tank 20 is V-shaped 29 and sloped 27such that the first end 31 of the V-shaped bottom 29 is lower relativethe second end 33 of the V-shaped bottom 29. Preferably, opening thefirst outlet valve 21 is aligned with the apex 30 of the V-shaped bottom29 in order to enable an unobstructed outward flow of the cleansingliquid 19 out of the filter tank 20 and into mud well 80. The backwashflow discharges directly into mud well 80 which is preferably positionedbelow filter tank 20 in order to enhance the cleansing action by thebackwashing liquid 19 upon the bottom 28 of the filter tank 20.

FIG. 4 illustrates a sectional view of the filter cell 34 illustrated atFIG. 1. Outer member 40 is spaced from the conduit 48 with the filteringmedium 46 positioned between the conduit 48 and outer member 40, thatis, in the volume between the outer member 40 and first portion 53 ofconduit 48 of the filter cell 34. Preferably, the outer member 40 of thefilter cell 34 is a screen with about 0.01 inch holes, the first portion53 of the conduit 48 is a P.V.C. pipe having a plurality of slits orlong narrow cuts or openings 56 with a width of about 0.01 inchestherein. Preferably, the filtering medium 46 is sand with an averagesize diameter of 0.02 to 0.03 inches. This size relationship enables theouter member 40 and first portion 53 of the conduit 48 to contain thefiltering medium 46 within the filter cell 34 during both the filteringprocess and backwashing process. The second portion 55 of the conduit 48extends into the backwash holding tank 60 to provide fluid communicationtherewith. During the filtering process the filtered liquid 18 travelswithin the passageway 49 of conduit 48. Whereas, during the backwashprocess, filtered liquid, characterized as cleansing liquid 19, isforced within the passageway 49 of conduit 48.

FIG. 5 illustrates a schematic fluid flow diagram of one embodimentusing the backwashing filter apparatus 10 in a sewage treatment plant 16operation. During the filtering process the liquid to be filtered 14enters the filter tank 20 by way of conduit 12. Conduit 12 optionallyincludes a valve 13 to control the flow from the sewage treatment plant16. Valves 21 and 76 are in a closed position and valve 64 is in a openposition during the filtering operation. The liquid to be filtered 14 isfiltered by filter cell 34 where filter clogging material such as slit,sediment and the like is separated by the filtering medium 46 from theliquid to be filtered 14 to produce a filtered liquid 18. The filteredliquid 18 flows into backwash holding tank 60 where the excess filteredliquid 62 drains through drain conduit 65 which is controlled by valve64. During the backwash process valve 64 is closed and valves 21 and 76are opened. Compressed air 78 enters the holding tank 60 forcing thefiltered liquid 18 back into conduit 48, into filter cell 34 and intothe filter tank 20. The backwashing liquid entering filter tank 20 thenflows out conduit 23 controlled by valve 21 into mud well 80 where it ispumped 86 via conduit 88 to the sewage treatment plant 16 for furthertreatment.

FIG. 6 illustrates a block diagram showing the interconnections of thecontrol unit 98 and the valves 21, 64 and 76 controlled by the output ofthe control unit. A timer apparatus 102 establishes the duration of thebackwashing process when activated by the control means 100. Optionalvalve 13, not shown, may also be controlled by control unit 98.

The manner of operation of the apparatus of FIGS. 1-6 will now bedescribed. During a filtering operation a liquid to be filtered isintroduced into the filter tank 20 by a conduit 12. The liquid to befiltered 14 reaches a first level 70 covering the filter cell 34. Theliquid to be filtered 14 radially flows inwardly through the outermember 40, and into the filtering medium 46 which entraps the filterclogging material forming a filtered liquid 18 which passes through aplurality of slits 56 formed in the first portion 53 of the conduit 48and into the passageway 49 of the conduit 48. The passageway 49 ofconduit 48 conducts the filtered liquid 18 into the backwash holdingtank 60 such that the filtered liquid 18 collects in the backwashholding tank 60 until the first level 70 is reached. At the first level70 the excess 62 filtered liquid 18 drains from the backwash holdingtank 60 through a second outlet valve 64 and into a filtered liquidreservoir 74. The filtering operation terminates when the level ofliquid to be filtered in the filter tank 20 reaches a second level 72indicating that the filtering medium 46 is clogged. The cloggedfiltering medium impedes the flow of the liquid to be filtered 14through the filter cell 34 causing the liquid to be filter 14 to rise toa second level 72 from the first or operating level 70.

An unclogging operation or backwash operation is commenced when thesecond level 72 is reached by opening the first outlet valve 21 of theof filter tank 20, closing the second outlet valve 64 of the backwashholding tank 60 and opening the inlet valve 76 to a compressed gas 78source. The incoming compressed gas forces the filtered liquid 18 in thebackwash holding tank 60, as a cleansing liquid 19, through conduit 48,through the plurality of slits 56 formed in the first portion 53 ofconduit 48 and through the filtering medium 46 whereby the materialclogging the filtering medium 46 is loosened and forced radially outwardfrom the filter cell 34, through the plurality of openings 42 formed inthe outer member 40 into the filter tank 20. The backwashing liquid 19from the filter tank 20 discharges through the first outlet valve 21thereby backwashing the filter cell 34 and the filter tank 20.

The preferred method of operation includes an automatic backwash control98 utilizing a float switch control means 100 to initiate the backwashprocess. The float switch control means 100 is positioned in the filtertank 20. The float switch control means 100 is activated when the secondlevel 72 is reached in the filter tank 20 thereby closing the secondoutlet valve 64 of the backwash holding tank 60, opening the firstoutlet valve 21 of the filter tank 20 and opening the inlet valve 76 ofthe backwash holding tank 60 to admit compressed gas into the backwashholding tank 60. A timing means 102 activated by the float switchcontrol means 100 terminates the backwash process by closing the firstoutlet valve 21, and opening the second outlet valve 64 and closing theinlet valve 76 after a preset period of time to enable furtherprocessing of filtered liquid 18.

In most applications of the apparatus of the invention the flow cominginto the filter tank 20 will be treated sewage treatment plant 16effluent. In this application a mud well 80 is positioned below thefilter tank 20 in order to take advantage of the backwash flow seeking alower level. Also, mud well 80 will include a pump 86 to return thespent backwash 84 to the sewage treatment plant 16 for furthertreatment.

In order to more specifically describe the above-described apparatus, afilter cell 34 is constructed using P.V.C. piping with a 2 inch outsidediameter as the conduit 48. Formed in the surface of a first portion 53of the P.V.C. pipe (conduit 48) are a plurality of 0.01 inch wide slits.A six inch diameter cylindrically shaped screen (outer member) 40 with0.01 inch holes about its surface is spaced apart in a coaxial mannerabout four inches from the first portion 53 of the conduit 48. A plug ispositioned at the opening at the first end 50 of the pipe 48 to preventdischarge of the filtered liquid through the opening and the ends 41,43of outer member are sealed relative the filtering medium to maintain thefiltering medium internal the outer member, thereby sealing 37,39 thefirst 36 and second 38 ends of the filter cell 34, respectively. Thefiltering medium is sand with an average diameter of 0.02 to 0.03inches. The sand is positioned in the cylindrical volume between theP.V.C. pipe (first portion 53 of the conduit 48) and the screen (outermember 40). This volume is the volume between the diameter of the outermember (6 inches) and the diameter of the conduit (2 inches) whenconsidered with the length of the filter cell. The length of the filtercell in the filter tank is about 72 inches. A mud well is positionedbelow the filter tank and in a manner which results in a downward slopeof about 6 inches of the filter tank toward valve 21. The filter tankbottom is V-shaped with the first outlet valve 21 positioned at the apex30 of the filter tank. The width of the filter tank is about 12 inches.The length of the filter tank is about 80 inches. A backwash holdingtank 60 is supplied for each filter cell 34 in order that each filtercell may be cleaned individually. The opening at the second end of theP.V.C. pipe 48 is open to enable the filtered liquid to drain into theholding tank. The backwash holding tank holds about 4 cubic feet offiltered liquid. The second outlet valve 64 is positioned proximate thetop of the backwash holding tank 60. The load on the filter cell isabout 2 gallons per square foot per minute per cell. During thebackwashing operation, compressed air is supplied at about 90 pounds persquare inch to the first inlet valve 76 on the holding tank 60. Theduration of the backwash process is about 1 minute.

It is to be understood that the apparatus of the invention may be builtto any desired size and capacity desired and the above description isnot limiting.

The filter cell of the invention enables the filtering capacity of thefiltering medium to be maximized by its radial placement about theconduit. That is, as a portion of the filtering medium becomes cloggedthere are numerous points about the circular surface area of the filtercell with remaining capacity to filter. Preferably, the second end 54 ofthe conduit 48 is positioned near the bottom 75 of the backwash holdingtank. This position maximizes the amount of filtered liquid to be usedas a cleansing liquid in the backwash process.

The composition of the filter tank, mud well and/or backwash holdingtank comprise concrete, fiberglass or the like. The outer member 40 ofthe filter cell 34 comprises any material such as aluminum, steel or thelike which is able to be fabricated to permit a plurality of openings tobe formed therein or can be configured into a screen or mesh with therequired plurality of openings for fluid passage through the outermember.

The conduit of the filter cell comprises a pipe or pipe-like structure.The most preferred plastic is P.V.C. (polyvinyl chloride), but otherplastics such as ABS (acrylo-nitrile butadiene-styrene), CVPC(chlorinated polyvinyl chloride) may be used. Also, other piping such assteel, copper or brass may be used. While the shape of the cross-sectionof the pipe may vary, the pipe used must structurally sufficient topermit a plurality of slits or long narrow cuts to be formed therein.

The size of the openings in the inner and outer member is determined bythe physical size of the filtering medium when the filtering medium isgranular.

The purpose of the openings in the conduit is to keep the filteringmedium external the conduit and to allow fluid communication between thefiltered liquid passing through the filtering medium and the hollowinner portion of the conduit of the filter cell during the filteringprocess. During the backwash process, the purpose of the openings of theconduit is to allow fluid communication between the cleansing liquid inthe hollow inner portion of the conduit and the filtering mediumexternal the conduit while maintaining the filter medium external theconduit.

The purpose of the openings in the outer member is to keep the filteringmedium internal the outer member and to allow fluid communicationbetween the liquid to be filtered in the filter tank and the filteringmedium of the filter cell during the filtering process. During thebackwash process the purpose of the openings in the outer member is toallow fluid communication between the radially outwardly flowingcleansing liquid and the filter tank while maintaining the filteringmedium internal the outer member. Therefore, the greater the physicalsize of the granular filtering medium, the greater the open area may befor individual slits and openings and still accomplish the above statedpurposes. The compressed gas used during the backwash process may be anycompressible gas, such as air, nitrogen or the like.

The filter and backwash apparatus requires that the outer member includeopenings be of a sufficient size to permit the retention of thefiltering medium internal the outer member while allowing fluidcommunication therethrough. The filter and backwash apparatus requiresthat the conduit include slits be of a sufficient size to permit theretention of the filtering medium external the conduit while allowingfluid communication therethrough.

The filtering medium may be composed of any material which is capable ofbeing held within the filter cell by the conduit and outer member andwhich filters sediment and the like from the liquid to be filtered. Thepreferred filtering medium is granular. The most preferred granularfiltering medium is sand. However, other granular filtering mediums suchas glass macrospheres manufactured by 3M Company may be used in theapparatus of the invention.

The control valves (first and second outlet valves and inlet valve) arethe "open-closed" type which may operate electrically of pneumatically.The control valves and the control float switch for activating controlvalves and the timing mechanism are conventional and known in the art.

The number of filtering and backwashing apparatus 10 used in thefiltering process is the number sufficient to filter the quantity ofinfluent delivered to the filter tank(s). Generally, the numbersufficient is that which allows the backwashing of at least one filterwhile maintaining sufficient filtering capacity to filter the influent.In the alternative, the influent to the filter tank may be terminatedwhile the backwashing process is taking place. If the rate of influentflow the filter tank is low, it need not be terminated during thebackwash process.

FIG. 7 shows the pressurized version of the filter and backwash process.As shown, the influent is pumped from tank 16 via pump 701 and conduit12. The suggested pressure is such as to maintain a pressure of 15 psiwithin filter tank 20.

Pressure switch 702 has pressure sensor 703 in communication with thepressure within filter tank 20. When this pressure rises beyond acertain point, say 20 psi, it is an indication that the filter isclogged. When this occurs, the backwash operation is started, undercontrol of controller 98 (FIG. 6) where the pressure switch takes theplace of switch 100. Under this arrangement, the water level shouldalways be full and thus a pressure reading triggers the backflushoperation, and not the high/low water reading.

During backflush, pump 701 should be reduced or turned off so as toreduce the pressure in the tank. This will allow a lower pressure on thecompressed gas. All other operation is the same as discussed previouslyfor FIG. 1.

By construction conduit 48 with an outer sliding conduit 704 havingslots 705 and 706 therein the effective size of each slot in conduit 48can be changed by sliding conduit 704 left/right. This covers/uncoversportions of the slots, thereby allowing less or more fluid flow into orout of conduit 48. This adjustment, while not necessary for operation ofthe system, can be important for fast and efficient backwashing.

Filter tank 20 should be vented through a valve 721 via pipe 720. Thepurpose of this venting is to prevent a vacuum from forming in thefilter tank during the backwash operation. This could be prevented bycontinuing the flow of liquid into the filter tank via conduit 12, ifdesired. Valve 721 is controlled by pressure switch 702 operating inconjunction with controller 98.

The physical shape of the inner and outer member is preferablycylindrical. Other shapes would be expected to be operable within theapparatus of the invention.

The present disclosure includes that contained in the appended claims aswell a that of the foregoing description. Although this invention hasbeen described in its preferred form with a certain degree ofparticularly, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed:
 1. A liquid filtering and backwashing apparatuscomprising:a filter tank having a first end and a second end to receiveunder a first pressure a liquid to be filtered; a filter cell to filterthe liquid to be filtered; a conduit having a first portion and a secondportion; said filter cell including said first portion of said conduitand an outer member with said outer member positioned around and spacedfrom said first portion of said conduit; said first portion of saidconduit and said outer member each being provided with a plurality ofopenings to enable fluid communication therethrough; said conduit havinga first end and a second end; said outer member having a first end and asecond end; said filter cell having a first end and a second end withsaid first end of said filter cell including said first end of saidouter member and said first end of said conduit and with said second endof said filter cell including said second end of said outer member; saidfirst portion of said conduit and said outer member of said filter celldisposed within said filter tank; a filtering medium positioned in usebetween said first portion of said conduit and said outer member toentrap filter clogging material from the liquid to be filtered therebyforming a filtered liquid; said first and second ends of said filtercell being sealed in use such that said filtering medium is containedbetween said first portion of said conduit and said outer member; abackwash holding tank to collect said filtered liquid; said secondportion of said conduit extending into said backwash holding tank toprovide fluid communication between said backwash holding tank and saidfirst portion of said conduit; said first end of said filter tankincluding means for enabling outward fluid flow from said filter tank toa reservoir; said backwash holding tank having a first outlet valve toenable said filtered liquid to drain from said holding tank; saidbackwash holding tank having an inlet valve to admit a compressed gasinto said holding tank after closing said first outlet valve of saidholding tank to enable backwashing of said filter cell and filter tank;a backwash outlet valve connected to said filter tank; a vent valveconnected to said filter tank; and a pressure switch control meanspositioned in said filter tank; said pressure switch being activatedwhen a second pressure in said filter tank is reached; and meansconnected to said activated pressure switch for closing said firstoutlet valve of said backwash holding tank, opening said inlet valve ofsaid holding tank to admit compressed gas into said holding tank,reducing said pressure of said received liquid to be filtered, openingsaid backwash outlet valve and opening said vent valve.
 2. The filterand backwash apparatus of claim 1 further including a timing meansactivated by said pressure switch control means to open said firstoutlet valve, to close said inlet valve, to close said backwash outletand vent valves, and to resume said first pressure on said receivedliquid to be filtered after a preset period of time to enable the liquidto be filtered.
 3. The filter and backwash apparatus of claim 1 whereinsaid reservoir is in fluid communication with a sewage treatmentfacility.
 4. The filter and backwash apparatus of claim 1 wherein saidopenings of said conduit are variable.
 5. The filter and backwash ofclaim 1 wherein said openings of said conduit are adjustable.
 6. Aliquid filtering and backwashing apparatus comprising:a filter tank forreceiving a liquid under pressure to be filtered; said filter tankincluding; means for enabling an outward flow from said filter tank; apressure switch for sensing pressure within said filter tank; a filtercell for filtering the liquid to be filtered; a conduit within saidfilter cell; a filtering medium positioned between said conduit and anouter member of said filter cell to entrap filter clogging material fromthe liquid to be filtered thereby forming a filtered liquid with saidconduit; said conduit being provided with a plurality of openings toenable fluid communication into said conduit while retaining saidfiltering medium external said conduit; a backwash holding tank tocollect said filtered liquid; said conduit extending into said backwashholding tank to provide fluid communication between said filter tank andbackwash holding tank; a mud well positioned below said filter tank forreceiving said filter clogging material from said filter cell; meansoperable under control of said pressure switch to admit compressed gasinto said holding tank to enable said mud well to receive said filterclogging material.
 7. A liquid filtering and backwashing apparatuscomprising:a filter tank for receiving a liquid under a first pressureto be filtered; a filter cell disposed within said filter tank; meansfor sensing pressure within said filter tank; venting means within saidfilter tank; a conduit; said filter cell including said conduit and anouter member with said outer member being positioned around and spacedfrom relative said conduit for receiving a filtering mediumtherebetween; said conduit and said outer member each being providedwith a plurality of openings to enable fluid communication therethrough;said conduit being in fluid communication with a backwash holding tank;a first outlet valve positioned in said filter tank to enable an outwardflow from said filter tank; said backwash holding tank having a secondoutlet valve to enable outward flow therefrom; said backwash holdingtank having an inlet valve to admit compressed gas into said holdingtank to enable backwashing of said filter cell and filter tank; andmeans operable under control of said pressure switch when said pressurein said filter tank reaches a second pressure for opening said inletvalve, closing said second valve and opening said first valve and forenabling said venting means.
 8. A filtering and backwashing methodcomprising:providing a liquid filtering and backwashing apparatusincluding a filter tank with a first outlet valve, a conduit, and anouter member around said conduit with a filtering medium positionedbetween said conduit and said outer member where said conduit isprovided with a plurality of openings to permit fluid communicationtherethrough, the outer member retaining filtering medium proximate saidconduit, said conduit and said outer member of the filter cell disposedwithin a filter tank and a portion of said conduit in fluidcommunication with a backwash holding tank having a second outlet valveand an inlet valve; and conducting a filter and backwash operationcomprising: introducing under a first pressure a liquid to be filteredinto the filter tank to reach a pressure to enable the liquid to flowinward through the plurality of openings of the outer member and intothe filtering medium which entraps the filter clogging material therebyforming a filtered liquid which passes through the plurality of openingsformed in said conduit; permitting the filtered liquid to be conveyed bysaid conduit into the backwash holding tank whereby the filtered liquidis collected; draining the filtered fluid from the backwash holding tankthrough said second outlet valve; periodically terminating the filteringoperation when the liquid to be filtered in the filter tank reaches asecond pressure in the filter tank indicating the filtering medium isclogged thereby impeding the flow of the liquid to be filtered throughthe filter cell resulting in the liquid pressure rising and conducting abackwash operation comprising: opening the first outlet valve of thefilter tank; closing the second outlet valve of the backwash holdingtank; opening an inlet valve from a compressed gas source to force thefiltered liquid collected in the backwash holding tank as a cleansingliquid into the conduit, through the plurality of openings of theconduit, through the filtering medium and through the plurality ofopenings of the outer member whereby the material clogging the filteringmedium is loosened and forced outward from the filter cell and into thefilter tank; reducing the pressure of said introduced liquid; anddischarging the cleansing liquid and clogging material from the filtertank through the first outlet valve thereby backwashing the filter celland the filter tank.
 9. The method of claim 8 wherein the apparatusincludes a pressure switch control means positioned in the filter tankto close the second outlet valve of the holding tank, to open the firstoutlet valve of the filter tank and to open the inlet valve of theholding tank to admit compressed gas into the holding tank, and toreduce said first pressure when the second pressure is reached in thefilter tank; anda timing means activated by said pressure switch controlmeans to close the first outlet valve, to open the second outlet valve,to close the inlet valve, and to resume said first pressure of saidintroduced liquid after a preset period of time to enable furtherpreparation of filtered liquid.
 10. The method of claim 8 wherein theopening sizes of said conduit are adjustable.